The present invention relates generally to gas turbine engines, and, more specifically, to combustors therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases that flow downstream through turbine stages which extract energy therefrom. A high pressure turbine powers the compressor, and a low pressure turbine produces useful work by powering an upstream fan in a typical turbofan gas turbine engine aircraft engine application, for example.
Combustor performance is critical to the overall performance of the gas turbine engine. The compressed air is mixed with fuel in the combustor for generating a fuel and air mixture which is ignited for generating the combustion gases.
For a typical annular combustor, a row of carburetors in the form of discrete swirlers and cooperating fuel injectors are used to mix the fuel and air prior to combustion, with the combustion gases being circulated downstream through the combustor for discharge to the turbines.
Combustor performance is in most part controlled by performance of the carburetors and involves many competing design objectives. Combustion must be suitably complete for reducing exhaust emissions, yet cannot be excessively lean to the point of flameout. The combustion gases require stable recirculation within the combustor without suckback or flashback into the individual swirlers.
Since the fuel and air are channeled into the combustor at circumferentially spaced apart discrete locations, variations in the fuel and air mixtures and resulting combustion gases occur both circumferentially as well as radially between the outer and inner combustor liners. Such variation must be minimized for improving performance and stability of the combustor.
And, the swirler itself requires precision in design and operation for mixing the compressed air with the injected fuel in a manner consistent with desired combustor performance.
Three basic types of air swirlers are known. In one design, a row of inclined primary apertures discharge jets of primary swirl air followed in turn by a row of secondary radial swirl vanes, i.e., jet-rad design. Fuel is injected at the center of the primary air jets, with the primary jets firstly swirling compressed air around the fuel, with the secondary radial vanes swirling additional air typically in counter rotation with the primary swirl air.
In a second known design, a row of primary radial swirl vanes replace the primary jets and operate in conjunction with the secondary radial swirl vanes, i.e., rad-rad design, for typically swirling the air in counter rotation around the injected fuel.
Another type of swirler design found in a double annular combustor includes primary axial swirl vanes cooperating with secondary radial swirl vanes, i.e., ax-rad design. In this design, the primary vanes directly receive the pressurized air under dynamic pressure thereof with axial momentum through the swirler. However, variations in the dynamic pressure of the compressed air around the circumference of each swirler and around the circumference of the double annular combustor causes variations in performance of the individual swirlers and in the resulting combustor performance.
The jet-rad design can cause uncontrolled fuel auto-ignition in high pressure ratio engines, and is therefore not preferred. However, the primary jets of swirl air promote stable recirculation zones of the combustion gases inside the combustor dome, and require minimum use of purge air through the fuel injectors.
The rad-rad design is considered superior in performance because it eliminates the cause of auto-ignition by eliminating zones of separated airflow caused by the discrete primary jets in the jet-rad design. However, the rad-rad design requires a large amount of purge air from the fuel injectors to produce axial momentum in the fuel and air mixture for establishing the desirable recirculation zone within the combustor dome.
Since the recirculation zone in the combustor is a key contributor to overall combustor performance, the particular design of the swirler affects combustor performance, requires compromise, and has associated advantages and disadvantages.
Accordingly, it is desired to provide an improved swirler for a gas turbine engine combustor for enhancing combustor performance while reducing purge air requirements, and also reducing manufacturing complexity and swirler cost.
A swirler includes a tubular body having a row of secondary radial swirl vanes. A tubular ferrule adjoins the body at the secondary vanes, and includes a row of primary swirl vanes. The primary vanes are disposed axially obliquely to the secondary vanes, with a common annular inlet facing radially outwardly for swirling air radially inwardly therefrom with axial momentum into the tubular body.